Bottles for carbonated drinks typically are made in a wide variety of sizes, including quite large sizes (e.g. 2 litre capacity). These bottles are required to meet rigorous testing standards to guard against the possibility that a bottle might leak or burst in use. The bottles are required to withstand severe, extraordinary mechanical impacts without leaking.
In order to ensure that the finished bottles meet the required standards, close attention is paid to the bottle manufacturing process. One expedient that is adopted is to make the finished bottle via an intermediate product known as a “preform”. Preforms are essentially elongate plastic tubes that are closed at one end and formed with a thread and collar at the opposite end that will become the neck of the bottle. The body of the preform is much shorter and of much less diameter than the eventual bottle and is usually reheated and then blow-molded to the final bottle shape and size.
Preforms typically are made by injection molding and are designed to have a molecular structure that results in the final bottle having the required strength characteristics. Attention must also be paid to the clarity of the plastic material of the preform, to ensure that the eventual bottle has the required visual characteristics. For example, the plastic material must not be allowed to crystallize, otherwise the preform will be “cloudy” and the quality of the eventual bottle will be impaired. Rapid post-mold cooling of the preforms is essential if the objective is to be met. Rapid cooling is also important in terms of cycle time and therefore productivity of the overall molding process.